Blank for eyeglass lenses having ellipse-like edge curves and means and method for selecting

Abstract

In eyeglass lenses which have a center thickness greater than the edge thickness in at least one cross section and different dioptric powers in different sections, round-blanks lead to ground eyeglass lenses which are of relatively high weight. The weight of such an eyeglass lens, and thus its center and edge thickness, is reduced if the blank is imparted a substantially elliptical edge curve. In order to reduce cost and expense, the dioptric range of the series of eyeglass lenses is divided into a predetermined number of ranges and a given type of edge curve is associated with each range. Within each range there are a number of centrally similar edge curves of different height and width for such type of edge curve. All edge curves are so selected that the eyeglass lens blanks provided with them have an edge thickness over the elliptical portion of their periphery which varies by less than 1.5 mm. An easily operated device is provided in order to select the optimal blank for mounting in an eyeglass frame.

What is claimed is: 
     
       1. A series of eyeglass blanks forming a collection from which one may select a blank suitable for making by normal finishing methods and without grinding a new surface on the blank, a finished eyeglass lens in accordance with a prescription which calls for a lens which (a) has a center thickness greater than its edge thickness in at least one cross section, and   (b) has different optical powers in different cross sections, and   (c) has dioptric powers within a substantial range of powers for which the series is designed, each blank in said series having an ellipse-like edge curve on at least partial regions of its periphery, said ellipse-like edge curve being so placed with respect to dioptric curvatures of said blank that the edge thickness of the finished eyeglass lens made from the blank varies by less than 1.5 mm throughout said ellispe-like edge curve, and the weight of the finished lens is substantially less than the weight of a lens of the same dioptric power made from a conventional circular blank.     
     
     
       2. The invention defined in claim 1, further characterized by the fact that the edge curves are ellipses the eccentricity of which lies between the values of 0.95 and 0.40. 
     
     
       3. The invention defined in claim 1, further characterized by the fact that the edge curve is developed as a circular arc in those portions in which the ellipse edge curves extend beyond the customary diameter of round-blank eyeglass lenses. 
     
     
       4. The invention defined in claim 1, further characterized by the fact that within each range there are provided a plurality of edge curves of different height and width which are centrally similar to a corresponding type of edge curve. 
     
     
       5. The invention defined in claim 1, characterized by the fact that the edge thickness of all eyeglass lenses lying within the same range varies by less than 1 mm throughout the elliptical peripheral portion of each lens. 
     
     
       6. The invention defined in claim 1, further including a plurality of series of blanks for a plurality of different ranges of dioptric powers. 
     
     
       7. The invention defined in claim 6, wherein one range (A) of dioptric powers includes powers from +0.25 diopters spherical to -1.75 diopters spherical combined with cylindrical powers varying from +2.0 at +0.25 sph. to +4.0 cyl. at -1.75 sph., and another range (B) includes powers from +0.5 sph. to +2.25 sph. combined with cylindrical powers varying from +1.5 cyl. at lower spherical values to +4.0 cyl. at higher spherical values, and a third range (C) includes spherical powers from +1.0 to +5.0 combined with cylindrical powers varying from +1.0 at lower spherical values to +4.0 cyl. at higher spherical values. 
     
     
       8. The method of selecting a most suitable rough blank from a series of different rough blanks having a different shapes and dimensions, for use in mounting on eyeglass lens of a certain prescription into a eyeglass frame, the method including the steps of: (a) providing a table of various dioptric combinations likely to be encountered in prescriptions;   (b) indicating on such table a limited number of ranges of dioptric combinations;   (c) providing a plurality of selecting devices, one for each of said ranges;   (d) each selecting device including (i) a base,   (ii) a disk rotatable on said base,   (iii) scale markings on said disk to indicate degrees of rotation of a cylindrical dioptric axis,   (iv) said disk being movable relative to said base to make an interpupillary setting,   (v) markings on said disk to indicate outlines of lens shapes and sizes appropriate to the particular range for which the selecting device is to be used, and   (vi) markings on said base for positioning thereon an eyeglass frame;     (e) positioning an eyeglass frame on the base of the selecting device appropriate for the range of said table which relates to the particular lens to be mounted,   (f) setting the disk of the selecting device to a desired interpupillary distance and a degree of rotation required by said prescription, and   (g) determining from the size and shape markings on the disk, with relation to said eyeglass frame, the proper size and shape of the rough blank to be used.   
     
     
       9. The method of preparing an eyeglass lens blank of the kind having a center thickness which is greater than its edge thickness in at least one cross section and having different dioptric powers in different cross sections, to furnish a desired one of a series of such blanks of different powers each of which blanks is ready for trimming by an optician to fit into a selected eyeglass frame to provide a trimmed lens of reduced thickness and weight as compared with a lens trimmed from a customary round blank of the same powers, without requiring any surface grinding of the blank or lens by the optician, which method comprises the steps of: (a) selecting a specific elliptical edge curve shape for a proposed blank having a specific spherical power and a specific astigmatic cylindrical power, said elliptical curve having a major elliptical axis extending in the same direction as the axis of said cylindrical power and a minor elliptical axis perpendicular to said major axis, said selected elliptical edge curve being selected to have at least a major part of its periphery lying within a circle defining a desired nominal diameter of the proposed blank notwithstanding that ends of the selected elliptical curve may lie outside of said circle, the selected elliptical edge curve having an elliptical eccentricity in the range from 0.9 to 0.5;   (b) selecting a proposed center thickness for said proposed blank such that a blank made of said elliptical shape and with said selected center thickness will have a minimum edge thickness at points where said minor axis intersects said edge curve and will have a variation of thickness of less than 1.5 mm over the entire elliptical part of the periphery within said circle; and   (c) producing a blank having the selected characteristics as defined in foregoing clauses (a) and (b);   (d) so that an optician to whom the produced blank is furnished may trim the edges of the produced blank to a shape to fit into an eyeglass frame, thereby providing an eyeglass lens of minimum thickness and weight without having to perform grinding operations on lens surfaces of the blank furnished to the optician.   
     
     
       10. A device for selecting the blank for an eyeglass lens of minimum weight from a series of eyeglass lenses which in at least one cross section have a center thickness which is greater than the edge thickness and different optical powers in different cross sections, said device being characterized by the provision of a table which divides the optical range of the series into a fixed number of ranges with each of which a type of edge curve is associated and by the provision of a number, corresponding to the number of ranges, of bases (6) each of which bears a family of edge curves which are centrally similar to the associated type of edge curve on a disk (7), which is rotatable on said base to a position in accordance with the axial position of the cross section of greatest optical power of the eyeglass lens a blank for which is to be selected, said base furthermore having reference lines (11) for the positioning thereon an eyeglass frame (12), into which the eyeglass is to be mounted.